The present invention relates to a system and a method for adaptive control of a lock-up clutch in a hydrokinetic torque transmitting unit.
Japanese Patent Application First Publication (unexamined) No. 63-172058 discloses a system for a control of a lock-up clutch in a hydrokinetic torque transmitting unit including a pump impeller, and a turbine runner. When it is engaged, the lock-up clutch connects the turbine runner to the pump impeller. The system comprises an electro-hydraulic circuit, including an electric actuator in the form of a lock-up solenoid, for hydraulically controlling engagement of the lock-up clutch, and a control unit for generating an operating signal supplied to the electric actuator. The duty of the lock-up solenoid is varied by the operating signal generated by the control unit. When duty of the lock-up solenoid is zero, the lock-up clutch is released. After the control unit starts generating the operating signal, the duty of the lock-up solenoid gradually increases since the operating signal is indicative of the duty determined in the control unit. After a time interval, engagement of the lock-up clutch is initiated, and when the duty attains a predetermined value, the lock-up clutch is fully engaged. Describing this process of engagement in other words, a slip in the hydrokinetic torque transmitting unit starts decreasing after the initial engagement of the lock-up clutch.
The present invention aims at improving a control of a lock-up clutch in a hydrokinetic torque transmitting unit such that a lag or delay before initial engagement of the lock-up clutch is kept at a target value. Thus, a variation in the lag owing to product to product variability or a change in temperature of hydraulic fluid is eliminated or minimized. If the lag is too long, baking of the lock-up clutch results, while if the lag is too short, a considerable shock results upon engagement of the lock-up clutch.
Therefore, an object of the present invention is to provide a system and a method for an adaptive control of a lock-up clutch in a hydrokinetic torque transmitting unit to compensate for a variation in lag owing to product to product variability, aging, a change in temperature of hydraulic fluid, and etc.